1. Field of the Invention
The present invention generally relates to charged particle beam lithography systems and, more particularly, to projection electron beam systems.
2. Description of the Prior Art
There is a continuing requirement to increase integration density of semiconductor integrated circuits to obtain maximum performance and functionality as well as maximum manufacturing economy. Accordingly, as practical limits of lithographic resolution using electromagnetic radiation (e.g. at deep ultra-violet (DUV and shorter wavelengths) for lithographic resist exposure has been approached, charged particle beams such as electron beams have been used to expose patterns on suitable resists even though such exposure tools require many sequential exposures to cover a chip area. To provide economically viable throughputs for charged particle beam exposure tools, projection systems have sought to shape the charged particle beam so that an increased number of pixels of the desired lithographic pattern can be exposed simultaneously and the number of sequential exposures correspondingly reduced.
Electron beam (e-beam) projection systems incur errors or noise in their deflection signals. These deflection signal errors result in placement errors in printed resist patterns (e.g. sub-field patterns) and, consequently, reduce product yield when projected sub-field images are not correctly stitched together. Some high throughput, state of the art electron beam lithography systems cover large fields corresponding to a large chip area while the feature size at the target/wafer is made smaller. For these state of the art e-beam systems, the electron beam deflection requirements are being driven to ever tighter specifications. However, noise makes these tighter deflection specifications increasingly difficult to achieve even with state of the art electronics.
For example, an electron beam projection system with a five millimeter (5 mm) deflection field and an error budget of five nanometers (5 nm) only allows an error of one part per million (1 ppm) for the entire deflection system. To produce a correct xe2x80x9ccurvilinear variable axis lensxe2x80x9d (CVAL) deflection path, which is preferred for such a system, requires more than 40 electronic drivers, each driver introducing some generally minimal but finite amount of noise and error. The individual errors from the electronic drivers are cumulative and, at best, the errors are additive. Consequently, the cumulative deflection noise is, in large part, the source of e-beam deflection error. Therefore, typical state of the art hardware, digital to analog converters (DACs), drivers, etc., in a state of the art CVAL cannot achieve the error budget specification required for degrees of integration density otherwise possible.
Thus, there is a need for reduced cumulative noise in deflection arrangements of e-beam projection systems in order to realize the benefits of highest practical degrees of integration density with acceptable throughput and manufacturing yield.
It is therefore an object of the present invention to reduce cumulative noise in deflection arrangements of charged particle beam projection systems.
It is another object of the present invention to eliminate noise sources in e-beam projection systems and deflection arrangements therein, in particular.
It is yet another purpose of the invention to improve curvilinear variable axis lens image location accuracy.
The present invention is a charged particle beam lithography system and deflection drive arrangement therefor wherein a common deflection signal is provided, simultaneously, to individual yokes and yoke drivers in an electron beam (e-beam) deflection apparatus. A single digital-to-analog converter (DAC) generates the common deflection signal. The common deflection signal is provided to individual programmable attenuators to adjust the signal for each individual yoke such that each individual signal is proportional to the common deflection signal. The adjusted individual signal is amplified and passed to one of the individual yokes. The yokes are controlled to provide curvilinear variable axis lens (CVAL) deflection that is adjusted to attenuate most of the noise from that which would have been present in a typical CVAL e-beam system.